Abstract: A discharge lamp in which fluctuation of the arc when the lamp starts and in which devitrification and damage of the arc tube are prevented, so that light intensity can be kept uniform over a long time is achieved by the cathode having a tapering part with a diameter which decreases in the direction to the tip that is formed with an area with different diameters extending around the tapering part in the peripheral direction which has concave-convex parts with groups of convex parts which are located next to one another in the axial direction of the cathode, the concave-convex parts in longitudinal cross section being arranged such that corner points of each convex part are located inside of an edge line of the tapering part, and an envelope curve which connects the corner points is convex with respect to the center line of the cathode.

Abstract: A discharge lamp in which fluctuation of the arc when the lamp starts and in which devitrification and damage of the arc tube are prevented, so that light intensity can be kept uniform over a long time is achieved by the cathode having a tapering part with a diameter which decreases in the direction to the tip that is formed with an area with different diameters extending around the tapering part in the peripheral direction which has concave-convex parts with groups of convex parts which are located next to one another in the axial direction of the cathode, the concave-convex parts in longitudinal cross section being arranged such that corner points of each convex part are located inside of an edge line of the tapering part, and an envelope curve which connects the corner points is convex with respect to the center line of the cathode.